This invention relates to monitoring structural members which are at least partially submerged in the soil bed material at the bottom of a body of water, such as bridge piers and footings, for scouring of the soil bed material around the submerged structure. More particularly, it relates to determining when the distance between a fixed point on the structural member and the top of the soil bed material is increased by removal of some of the soil bed material during the scouring process.
As referred to herein, "scouring" is the movement of material in the soil bed of a body of water, which movement is caused by the combination of a high water level and movement of the water at an above normal velocity. Scouring typically occurs in stream and river bottoms during periods such as heavy rainfalls and spring runoffs. Under some conditions, scouring can create cavities having depths of two times the depth of the body of water while the scouring is occurring.
Because many bridges over streams and rivers are supported by piers and abutments which rest on footings which are at least partially submerged in the soil bed of these bodies of water, scouring is a major factor in the safety of these bridges. If the scouring action continues for a long enough period of time, the bridge footings and piers can be undermined to the extent that the bridge structure fails. Because scouring is of such concern, the routine bridge safety inspections that most bridges are periodically subjected to include underwater inspection of the bridge piers and abutments to check for evidence of past or present scouring.
However, past instances of scouring can often go unnoticed even during these underwater inspections. Typically, when the high water level that caused the scouring recedes and the water flow velocity returns to normal, the scoured area is refilled by deposits carried by the receding waters. A soil bed area that has been scoured and then refilled in this manner can appear very similar to a soil bed area that has not been disturbed by scouring, making past instances of scouring very difficult to detect even using periodic underwater inspections. Additionally, even if no scouring had occurred up to the time of the inspection, scouring action could begin the day after the inspection if the water level and flow velocity suddenly increased. Thus, the type of underwater inspections currently employed to monitor scouring are only minimally effective.
Moreover, even though scouring is very evident while it is occurring, underwater inspection of bridge piers and abutments during the water level and flow conditions that exist while the scouring is proceeding is not practical. Not only are such conditions hazardous to the safety of the divers conducting the inspections, but the high water level, high flow velocity, and poor visibility associated with the scouring conditions make it nearly physically impossible to conduct an effective inspection.
Thus, although beneficial steps could be taken to minimize the stresses on the bridge structure during the scouring period and remedial action could be taken to protect the structure after the high water receded, if only scouring could be detected when it was occurring, methods and apparatus for doing so are not presently available.
Accordingly, it is an object of the present invention to provide a method for monitoring scouring around a submerged structural member without requiring underwater inspection.
It is another object of the present invention to provide a scour monitoring method which can be employed to check for scouring as frequently as is required to ensure the safety of the bridge, including the ability to continuously monitor for scouring if necessary.
It is also an object of the present invention to provide a means for detecting the occurrence of scouring even if the scoured area is later refilled.
It is a further object of the present invention to provide apparatus for monitoring scouring which is relatively inexpensive and easy to install and operate.